Evaluating different double-stranded RNA structures for their ability to control pest flea beetles
Canola is an economically important Canadian crop that suffers significant annual losses by damage from feeding flea beetles (Phyllotreta cruciferae and P. striolata). Increasing incidences of resistance and concerns about off-target effects with current insecticides demands new methods of control. Recently, environmentally safer approaches to pest control have been investigated using RNA interference (RNAi), a sequence-specific gene silencing mechanism triggered by exogenous double-stranded RNA (dsRNA), to selectively induce the mortality of targeted species. This study examined three different dsRNA structures for their ability to kill P. striolata flea beetles and thereby reduce feeding damage on canola leaves. Long linear dsRNAs (212-214 bp), short hairpin RNAs (hpRNAs) (21-24 bp), and short paperclip RNAs (pcRNAs) (21-24 bp) targeting mRNAs of three essential genes, Ras opposite (Rop), Sec23, and Snf7 in P. striolata were investigated. P. striolata adults were fed dsRNA-treated canola leaf disks, and impacts on insect survivorship and leaf material consumption were recorded over an eight-day period. pcRNAs targeting Sec23 and Snf7, and long dsRNAs targeting Sec23 and Rop effectively killed flea beetles, resulting in the reduced consumption of treated canola leaf tissues. Consumption of both the Sec23-specific long dsRNA and pcRNAs caused similar levels of flea beetle mortality (68% and 76%, respectively), whereas only the Rop-specific long dsRNA and the Snf7 pcRNA were effective at killing the beetles (76% and 84%, respectively). hpRNAs proved the least effective across all gene targets, killing at most, between 40-52% of flea beetles, depending on the gene target, and in general, these values were not significantly different relative to the negative controls. While this study examined dsRNAs specific for only three target genes, it provides evidence that RNAi-based pesticides have the potential to control these economically important pests and that short pcRNAs can be as effective as conventional long linear dsRNAs.
flea beetles, Phyllotreta cruciferae, Phyllotreta striolata, RNA interference, RNAi, dsRNA, double-stranded RNA